非均质条件下锶迁移的反向随机模拟

通过重新分析用于模拟降雨入渗和示踪剂释放迁移的室内土柱(填装砂土和黏土)实验,基于对流弥散方程(ADE)和连续时间随机游走(CTRW)理论的模型,对实验穿透曲线进行了反向模拟,定量分析了锶(模拟~(90)Sr)的non-Fickian弥散迁移规律。结果表明,由于粒子扩散进入不流动区和吸附到矿物表面等因素的影响,从土柱中淋滤出来的溴和锶的最大质量份额分别约为60%和50%,此外,流出曲线不同程度的早到和拖尾特征也表明,土柱实验中存在优先流现象。CTRW模型考虑了水力-化学耦合效应过程,较好地描述了锶的non-Fickian迁移(0β2)和Fickian迁移(β2)行为,non-Fickian弥散迁移可归结于土柱结构非均匀性导致的流场变化(如优先流)和复杂的吸附过程,特别是,锶在黏土矿物中吸附导致了其峰值浓度的降低和延迟,进一步增加了non-Fickian迁移。

Random Inverse Modelling of Strontium Migration in Heterogeneous Media

In the context of rainfall infiltration and source term release scenario,the non-Fickian dispersive migration behaviour with sorption of strontium (analogue for 90Sr) in column experiments was investigated.Based on equilibrium advection-dispersion equation (ADE) and continuous time random walk (CTRW) framework,inverse modelling was conducted to re-evaluate the breakthrough curves (BTC).The results show that because of the molecular diffusion into/out immobile zone and mineral sorption effect on the clay surface,approximately 60％ of bromine and 50％ of strontium can be eluted from the columns.In addition,early breakthroughs and late tails of BTCs in varying degrees indicate the occurrence of the preferential flow.CTRW model,which considers essentially the hydraulic-chemical coupling effect,can preferably describe non-Fickian migration with 0<β<2 and Fickian migration with β>2 for strontium.Furthermore,in packed columns,non-Fickian migration phenomenon can be attributed to local flow field variation (eg,preferential flow) due to the non-uniformity of soil structure and complex sorption process.Specifically,the additional adsorption of strontium on clay minerals induces the reduction and delay of the peak concentration,and thus enhances the non-Fickian migration process.